Tegel points to institutional design. In particular, Peru has a hybrid presidential/parliamentary system with a dual executive, which he argues "serves both to institutionalize conflict and prevent fresh
voices with public backing from entering the political arena." Congress has outsized power that has consistently crippled the president. That system is also why PPK pardoned Alberto Fujimori.

Further, Peru has a unicameral legislature, which when combined with high threshold for parties to even register, has fostered legislative dominance in many ways. Thinking again of PPK, it meant that Congress could use impeachment as extortion. And good luck getting electoral reform through that body.